I want to offer this in a respectful manner - it's taken from a Geopolitical Futures (GPF) article - and it's an assessed opinion about Europe and the EU - the topic was whether the EU acts like a country or not
"The EU, however, is not a country, and it is not about to become one. If Europe were a country, German tax dollars would be allocated toward paying down Greece’s debt. If Europe were a country, its military would be deployed in Poland to defend its borders from Russia. If Europe were a country, rules would apply equally to all: France wouldn’t get to ignore European budget deficit rules and then single out Poland as a black sheep for violating democratic norms because of its judicial reforms. If Europe were a country, a Romanian would be willing to die to protect a Spaniard. I have no doubt that there are people of goodwill in all these countries, none of whom wish to see harm visited upon others. But there’s a difference between passive hope for all to live in peace, and active sacrifice to protect members of the same community."
I'm sure there are differing opinions, but I think this wraps up what the issues are - and why so many people supported Brexit.